Manufactures and developers of absorbent articles have traditionally relied upon results from physical testing of prototypes as a basis for evaluating the performance of absorbent articles and as a basis for making design changes. Developing prototypes of absorbent articles can be expensive because the equipment necessary to manufacture the absorbent article may not be developed at the time when new absorbent articles are being developed. In some instances, the materials from which the absorbent article will be constructed have yet to be developed. Furthermore, physical testing often requires working in a controlled laboratory environment, which can be expensive. In the case of hygienic products, such as catamenial devices, wound dressings, facial tissue, diapers, and diaper wipes, laboratory personnel may be exposed to increased risks to their health as a result of handling animal exudates during laboratory tests. For absorbent articles designed to absorb other materials, physical testing may require that laboratory personnel be exposed to unhealthy chemicals that the absorbent article is designed to absorb.
Obtaining data describing the transient behaviour of absorbent articles can be challenging. Often, a designer of absorbent articles is interested in how the absorbent article acquires fluid at the onset of exposure to a fluid. By the time the designer removes the absorbent article from exposure to the fluid, dissects the absorbent article, emplaces portions of the absorbent article and measures the distribution of the fluid therein, the distribution of the fluid can change significantly as compared to the distribution of fluid when the absorbent article was removed from contact with the fluid.
In some design processes for designing absorbent articles, physical testing on replicates of absorbent articles is needed to deduce conclusions based on observed results from testing. Testing replicates can help reduce uncertainties in making evaluations of different designs for absorbent articles and making decisions on how to improve designing of an article. Creating prototypes that are precise replicates of one another can be challenging, but when prototypes are not precise replicates of one another, interpreting testing results can be more difficult.
Absorbent articles are often designed to absorb a variety of substances. The substance may be a fluid containing only a single constituent, such as water. The substance may be a multi-phase fluid such as human menstrual fluid animal menses or bowel movement material. Physical testing of prototypes of absorbent articles exposed to substances comprising multiple components in multiple phases can be problematic, because the designer of the absorbent article may be unable to identify the particular impacts of specific phenomena on the performance of the absorbent article. Furthermore, the testing equipment used to test absorbent articles is often designed to test the absorbency with respect to clean water, rather than a substance containing a variety of solid, organic or inorganic fluid, and gaseous phases.
The fluid transport properties of absorbent materials commonly used in absorbent articles can be difficult to measure. Key fluid transport properties, which partially describe interactions between the absorbent and fluid, include the capillary pressure as a function of saturation and the relative permeability as function of saturation. Most commonly used methods for measuring the absorbent-fluid interaction properties are not suitable for testing with fluids other than water. Thus, there is a continuing unaddressed need for methods for developing absorbent articles that integrates physical measurements of the absorbent properties of absorbent materials into the design process. Additionally, there is a continuing unaddressed need for virtual product development methods that allow for the product developer to gather data on the transient performance of an absorbent article. Further, there is a continuing unaddressed need for methods for developing absorbent articles that do not rely entirely on physical testing of prototypes. There is also a continuing unaddressed need to be able to test absorbent materials and designs for absorbent articles without having to expose personnel to the substances absorbent articles are designed to absorb. Furthermore, there is a continuing unaddressed need for methods for measuring the capillary pressure versus saturation function for fluids other than water.
Co-pending U.S. application Ser. No. 11/504,993 filed on Aug. 16, 2006, now U.S. Pat. No. 7,684,939, describes a model and method to design articles with a certain fluid acquisition, solving the equation of continuity and partially saturated flow in porous media (also known as the Richard's equation). For absorbent articles that comprise fluid-swellable material (e.g., superabsorbent material or hydrogel-forming materials that absorb liquid due to an osmotic pressure gradients between the material and the surrounding fluid and that subsequently swell upon absorption), the traditional Richard's equation may no longer be sufficient to desirably describe the fluid flow through the swelling and/or swollen structure formed by the particles. In fact, the swelling process is an important factor because it can cause the structure to increase its thickness significantly, even (e.g.) 10 to up to 100 times. Such swelling may lead to changes of intrinsic properties such as permeability, capillary pressure and/or porosity. It is believed that such changes are controlled by the swelling kinetics of the water-swellable material in the product structure. Thus, there is a need for a design method to design absorbent articles comprising fluid-swellable composite material as mentioned above.